I get on the 7.49 TGV at Béziers to Paris. I am in a window seat and quickly fall asleep. I register at Montpellier that someone comes and sits next to me but fall asleep again and wake up an hour or so later. I study my neighbour. From what I can see he is very good looking in a distinguished sort of way. He is reading an extremely intellectual looking book. I pretend to stretch and look around the carriage so I can get a better look at him. “Did you sleep well?” he asks.

We spend the rest of the journey talking. B, as I will call him, tells me he is an MP and on his way to the Assemblée nationale. He asks me why I am going to Paris. “I’m going to write about French women and lingerie,” I tell him.

“And is this a subject of which you know much?”

“Not yet . . . but I’m hoping to learn.”

B tells me the most important thing to understand about women and their lingerie is that they wear it for themselves and not for men. He drops me off in a taxi at my hotel in Saint-Germain. We exchange cards. “J’ai été ravi d’avoir fait votre connaissance,” he says when we part. “Call me if you ever need anything in Paris.” He kisses my hand and gets back in the taxi.

The reason I’m researching underwear is that, having lived in France for five years, I want to be able to walk into a room and not be immediately recognised as an English woman. I want the indefinable and alluring chic that French women have. Underwear is a lot more important to French women than it is to your average English girl, or at least this average English girl. Prior to moving to France it really wasn’t an issue I had thought that much about.

French women don’t mind spending money on underwear. A woman I meet in Paris who has been a mistress for 15 years says she devotes 90% of her salary to it.

I begin at Galeries Lafayette, one of the biggest department stores in the world. The first person I accost is English. “It’s unbelievable,” says Samantha, who is from Hull. “I used to work at Selfridges and we had about a third as much space dedicated to underwear.”

Historically, the French have always been ahead of the British in terms of underwear. They were wearing knickers way before us. In the 16th century Queen Catherine de Medici introduced them as she preferred to ride side saddle to show off her legs and needed to protect herself from the elements.

The Brits still thought panties scandalous and only fit to be worn by prostitutes. Knickers weren’t really accepted until the 19th century when the Victorians seized upon them as a good thing. The brassière was invented by Herminie Cadolle, who exhibited it at the 1900 Great Exposition and became a fitter of bras to the elite of the day, including Mata Hari.

I speak to some other shoppers and ask them what they look for. “I buy nice underwear in order to look sexy when I take my clothes off,” says Claire, a 42-year-old Parisienne.

“It’s what I put on next to my skin, so it has to be perfect,” says Julie, 28, from Amiens.

The changing rooms are sumptuous. There are two buttons on the wall; one summons an assistant to help you with sizes and styles. The other changes the light inside the cubicle from day to night, so you can see at the flick of a switch how your new bra will look when your lover undresses you. I spend at least two happy hours flicking the switch on and off in several ensembles. I wonder briefly what B’s tastes in underwear are. Then it’s back to work.